Activated Carbon Filters

Using the STS Siloxane Monitor on sites with Activated Carbon Filters.

Activated carbon filters work by passing the biogas derived from the AD plant through a metal tower filled with activated carbon. Normally the gas will have been dried by running through a chilling plant to remove excess water which would be absorbed by the Carbon.

The siloxanes and other contaminants are trapped by the carbon allowing the filtered gas to pass through and into the engine. The size and design of Carbon filters will depend on the site specifics, flow and anticipated Siloxane loading, often sites will implement a set of towers in series which are rotated to get best optimisation of the Carbon.

The issue here is that optimisation is based on a very small subset of data taken from bag samples submitted to the lab for analysis which have been shown to be subject to influence from time and temperature causing condensing of the siloxanes onto the bag walls and a resultant variable result.

In house tests by STS managed to achieve figures of +/- 100% by manipulating these factors.

Bag analysis is also relatively expensive so users tend to do as few tests as they can - and then rely on the results to produce a schedule for changing the filters. In a perfect world that would be fine, but that assumes no change in the loading of siloxanes received into the plant and a consistent performance of the Carbon and consistent water removal from the gas stream - three things which simply don't happen.

The solution is to monitor the gas flow to the engine post filter on a regular basis, in the case of the STS Siloxane Monitor that is hourly.

This provides the user with a constantly updated dataset on which to make informed decisions regarding the correct time to replace the filters.

This is a win-win situation, changing the filters too early when Siloxane breakthrough has not occurred will cost unnecessary money and changing the filter too late when breakthrough has already occurred will costs even more money in damage to engine components and degradation of engine oil quality and life time.